Production of cellulose pulp



Oct. 31, 1933- o. v. E. JANSA ET AL 1,933,017

PRODUCTION OF CELLULOSE PULP Filed Jan. 15, 1932 Patented Oct. 31, 1933 UNITED STATES PRODUCTION OF CELLULOSE PULP Oscar Victor Emanuel Jansa and Erik Gunnar Planck, Stockholm, Sweden Application January 15, 1932, Serial No. 586,834, and in Sweden January 19, 1931 12 Claims.

The present invention is for improvements in the production of cellulose pulp and relates particularly to chemical treatment of vegetable fibres by continuous digestion or cooking.

In the production of cellulose pulp the raw material, i. e. Wood or other vegetable fibrous material, is treated with a'decomposition or lixiviation liquor in containers or digesters under pressure and at elevatedtemperatures. 'Hitherno to this digestion or lixiviation has been carried out discontinuously. This method, however, has serious disadvantages such as are incident to all discontinuous processes, for example that the consumption of raw material and lixiviation 115 liquid as well as heat is variable and that it is necessary to store these materials and the heat as well as the final product. Further, a considerable amount of heat is lost in emptying the contents of the boiler and it is diflicult to satisfactorily control and regulate the decomposition.

The digestion therefore becomes uneven, the quality of the resulting product is non-uniform and fibres are lost.

' These disadvantages may be avoided if the cooking is made continuous.

However, a continuous method of producing cellulose pulp has not yet been found practicable in the industry, in spite of the considerable number of methods which have been patented. This shows that in actual practice there are certain dificulties which have not yet been overcome.

.The main difliculty in the solution of this problem is the continuous introduction of the wood or-other fibrousmaterial into the digester, and all of the known methods have failed in this respect, :i. c. it has been impossibleor impracticable tocontinuously introduce the raw material into the digester in such a way that the required pressure of" 5-10 atmospheres above the atmos- 4o pherio pressureis-maintained. I

It has been suggested, for example, to'finely divide the'r'aw material before the digestion, so asto bring it into a state similar-to that of finely divided sawdust inorder to obtain by mixing it With aliquid a mass'of so freely flowing consistencyas to enable it to-be pumped into-the digester with, for .examplaan ordinary piston pump. -As a .result of this fine. division of. the fibrousmaterial the valuable cellulose fibre-is destrnyed." .I

it has also been suggested to predigestthe fibrous material in special softening containers andafter it has been mixed with the suitable amount of lixiviation liquidfor-the digestion to 2' fioree it into the digester by means of cooperating screws, the idea being that the fibrous material compressed to a stopper at the inlet of the boiler should provide the required sealing. It is evident, however, that in the practical operation of such a process it will be impossible to obtain by means of a moving stopper of moist fibrous material a seal which is effective against such considerable pressures as 5-10 atmospheres.

It has further been suggested to use cooperating piston, valve, sleeve and lever arrangements etc., as well as other more or less complicated arrangements of more theoretical than practical value.

According to the present invention the fibrous material is introduced into a container or digester together with a liquid, lixiviation liquid or. other liquid, for example Water, a sufiicient amount of liquid being used to enable the feeding to be carried out by such means as a centrifugal pump, ejector, injector or'the like. After the mixture has been introduced into the digester the excess of liquid is separated to be used for the introduction of new material; the energy of the separated liquid may be utilized for pumping the mixture into the digester. No special pretreatment of the fibrous material is required before it is introduced into the digester and it is possible to use coarser chips than that at present employed in the wood pulp industry and to continuously feed this into the boiler. The size of the chips which can be used depends only on theeffect'of the size on the quality of the final product, i. c. it can'be chosen with regard only to the quality of the final product. i

In the accompanying drawing some forms of apparatus are shown which may be used for carrying the invention into effect:

Fig. 1 shows an arrangement for feeding the fibrous material into the digester by'means of a centrifugal-pump. l is a mixing vat to which the wood chips are supplied by means of the conveyor 2 and the liquid is supplied through the conduit 3. By means of the centrifugal pump 4 the mixture of liquid and chips is raised through the conduit 5 to the sieving chamber 6, in which excess of liquid is'separated and returned to the mixing-vat 1 through the conduit -'7, the energy of this liquid being utilized in an ejector 8 for reducing the height which theliquid' has to be raised by the pump. The conduits 5 and 7 are providedwith closing valves 9 and 10 which prevent the contents of the digester from escaping when the pumping is interrupted.

The chips separated from the excess of liquid are 'carriedfrom the sieving chamber 6 into the digester 11 by means of the pressure of. the following material. The required amount of lixiviation liquor is supplied through the conduit 12 and the required heat through the conduit 13. When the digestion is completed the contents of the digester is continuously drawn off through the conduit 14.

Fig. 2 shows a modification of the arrangement shown in Fig. 1, in which the pressure energy of the separated liquid is utilized in a turbine 15 which is preferably mounted on the same shaft as the pump 4 and the motor 16.

Fig. 3 shows an arrangement for feeding the fibrous material into the digester by means of an injector. The excess of liquid separated in the sieving chamber 6 is passed through the conduit 7 to a pump 17, which forces the liquid to the injector 18 arranged in the mixing vat 1, which presses the mixture of chips and liquid through the conduit 5 to the sieving chamber 6, and so on.

Fig. 4 shows a modification of the arrangement shown in Fig. 3, in which the excess of liquid separated in the sieving chamber 6 is passed through the conduit 7 to a steam injector 19 which forces the liquid to the ejector 18 arranged in the mixing vat l, which in turn forces the mixture of chips and liquid through the conduit 5 to the sieving chamber 6, and so on. Steam is supplied to the injector 19 through the conduit 20. For cooling of the excess of liquid drawn off from the sieving chamber 6 the conduit 7 is provided with a heat exchanger 21 which may be used for preheating the lixiviation liquid supplied through the conduit 12, as shown in the figure.

Fig. 5 shows an arrangement for introducing the fibrous material into the digester by means of a steam ejector. The figure shows an embodiment in which the fibrous material is introduced into the digester by means of two ejectors 22 and 23 working in series. Steam is supplied to the ejectors by means of the tubes 24 and 25. The fibrous material may be supplied to the digester with or without liquid. In the latter case the air is expelled from the fibrous material by means of steam, which is supplied to the steam sieving chamber 27 by means of the conduit 26, said ch mber being arranged in the lower part of the mixing vat 1.

It will be apparent that many other modifications of the invention are possible within the limits of the invention as set forth in the annexed claims.

By means of the method described above the material may be introduced into the digester at any working pressure and the method may therefore be used in combination with practically any of the known processes for digestion of wood pulp. Further, any type of digester may be used and the digesters now employed may easily be converted for continuous operation. The digester shown diagrammatically in the figures, comprising an outer and an inner tube, is of particularly great advantage with regard to heat economy, provision being made for heat exchange according to the principle of counter current, further it is easy to control and regulate the process etc. In consideration of the high pressure maintained in the digester the outer tube is preferably made cylindrical, whereas the inner tube may have a varying section, which has the advantage of a perpetual mixing of the material and a velocity of flow through different parts of the digester according to the velocity of the reaction. The digester may be arranged horizontally, vertically or at any desired angle. The two latter positions have the advantage that any gas liberated may easily be dispelled from the upper part of the digester, to be used again in the process if desired,

and further the completely digested cellulose pulp, as a result of the higher specific .gravity thereof,

collects at the exit end of the digester. The heat required for carrying out the digestion is supplied to the digester in one or more sections as known per se either directly or indirectly by means of gas, steam or liquid.

A simple and effective control of the operation of the process may be obtained by providing in one or more sections of the digester registering or non-registering apparatus of known types for determining for example the pressure or temperature of the contents of the digester or for analyzing the lixiviation liquid, the fibrous material or the cellulose. The digested cellulose pulp may be withdrawn from, the digester continuously by means of back pressure-producing nozzles, blade wheels, piston devices etc. connected in series or in parallel.

What we claim is:-

1. In a method of continuously digesting vegetable fibrous material by treatment with a lixiviation liquor in a digester under pressure and at elevated temperatures, the improvement which consists in introducing the raw material into the said digester in admixture with an excess of liquor and then separating the excess of liquor from the fibrous material and withdrawing it from the digester.

2. In a method of continuously digesting vegetable fibrous material by treatment with a lixiviation liquor in a digester under pressure and at elevated temperatures, the improvement which consists in introducing the raw material into the said digester in admixture with an excess of liquor, separating the excess of liquor from the raw material, withdrawing it from the digester and 1 5 using it again as the vehicle for the introduction of new raw material.

3. In a method of continuously digesting vegetable fibrous material by treatment with a lixlvlation liquor in a digester under pressure and at elevated temperatures, the improvement which consists in introducing the raw material into the digester in admixture with an excess of a fluid and then separating the excess fluid from the fibrous material and withdrawing it from the digester.

4. In a method of continuously digesting vegetable fibrous material by treatment with a lixiviation liquor in a digester under pressure and at elevated temperatures, the improvement which consists in introducing the raw material into the said digester in admixture with an excess of liquor, separating the excess of liquor from the raw material, withdrawing it from the digester and using the energy thereof for the introduction of new material into the digester.

5. In a method of continuously digesting vegetable fibrous material by treatment with a lixiviation liquor in a digester under pressure and at elevated temperatures, the improvement which consists in introducing the raw material into the said digester in admixture with an excess of liquor, separating the excess of liquor from the fibrous material, withdrawing it from the digester and utilizing the energy thereof in a liquid turbine.

6. In a method of continuously digesting vegetable fibrous material by treatment with a lixiviation liquor in a digester under pressure and at elevated temperatures, the improvement which 150 consists in. introducing the raw material into the said digester in admixture with an excess 0! liu= uor, separating the excess of liquor from the fibrous material, withdrawing it from the digester and utilizing the heat thereof for preheating the lixiviation liquor,

1 Apparatus for digesting vegetable fibrous material comprising a digester, a supply of said fibrous material, a supply oi a fiuid under pres= sure, means for said fibrous material and said fluid, means for forcing the resulting min ture into the disaster under pressure, and means for separating the fibrous material and the fluid and for withdrawing the latter from the dlgester.

8. Apparatus as defined in claim '21 comprising means for returning the fluid withdrawn from the digester to the means for mixing said fluid with the fibrous material.

9. Apparatus as defined in claim 7 in whichthe means for forcing the mixture of fibrous material and fluid into the digester comprises a pump.

Ml. Apparatus as defined in claim Z in which the means for forcing the mixture oi fibrous material and fluid into the digester comprises an injector 11. Apparatus as defined in claim '3 in which the means for forcing the mixture of fibrous material and fluid into the digester comprises a pump and an injector connected to operate in series.

12. Apparatus as defined in claim 7 in which the means for forcing the mixture of fibrous materiai and fluid comprises a plurality of injectors operating in series oscas, VICTOR Em muss. mm comma 

